Kate – who is pregnant with her child with Prince William – was admitted to St. Mary's Hospital, Paddington in London earlier this morning (April 23).

The 36-year-old royal travelled by car from Kensington Palace to the Lindo Wing at St. Mary's Hospital with William.

Kate has been on maternity leave since making a last royal visit to a charity lunch on March 22, although she and Prince William made an unexpected appearance at the annual Easter church service in Windsor on April 1.

The Duke and Duchess are parents to Prince George, 4, and Princess Charlotte, 2.

Kate previously gave birth to George and Charlotte at the Lindo Wing at St Mary's Hospital.

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Meanwhile, following arrival of royal baby number three,the Queen must always be the first person to hear news of the baby's safe delivery.

Following this, Prince William and Kate will be given a few hours to bond with their new baby in peace (as well as to inform immediate family and loved ones). After this time, a press release will be sent out to media organisations via email containing information about the time of birth as well as the gender of the royal baby.

This press release will be swiftly followed by announcements containing similar details on the official Kensington Palace Twitter and Instagram accounts.

Then comes the traditional formality of placing the birth announcement on an easel outside Buckingham Palace.

The announcement – which in times gone by was hand-written, but nowadays is typed up – also confirms the gender, time of birth, and that both mother and child "are doing well".

It is then signed by doctors at the hospital, and is safely delivered back to the palace by car.

Excited royal fans often line up outside the palace to witness the easel for themselves.